WO1991003434A1

WO1991003434A1 - Sheet material handling apparatus

Info

Publication number: WO1991003434A1
Application number: PCT/GB1990/001349
Authority: WO
Inventors: Robert Mcnab Mckill; Charles Roger Mortimore; Terence Edward Neil
Original assignee: Abracad Systems Limited
Priority date: 1989-08-31
Filing date: 1990-08-31
Publication date: 1991-03-21
Also published as: GB8919672D0; AU6354790A

Abstract

Sheet material handling apparatus for loading sheets of glass on a stacking arrangement comprises an inspection table (10) on which each sheet of glass is measured. The glass is aligned for measurement with one lateral side of the table by being transported laterally by conveyor belts (30). After measurement the glass is moved on a conveyor (12) serving a set of loading stations (14). The side of the inspection table is defined by a set of rollers (65) which side is in line with the edge of the conveyor which is defined by guide rollers (66). Passing the laterally aligned glass from the table to the conveyor ensures that it is correctly laterally positioned for transfer to an upright loading frame by means of rotatable loading arms (26).

Description

SHEET MATERIAL HANDLING APPARATUS

This invention relates to apparatus for handling sheet material, for example, semi-rigid or rigid sheets, such as plate glass.

For some time, glass in sheet form has been supplied to glass distributors from the manufacturer in the form of large (approximately 6m x 3m) plates. The size is commonly referred to as a "jumbo" sheet. It is the job of the distributor to store the glass and cut these large sheets as economically as possible into various smaller sizes according to demand.

For handling and cutting up the glass, numerically controlled (NC) diamond cutting machines are used. A jumbo sheet is taken off a stack and laid down flat on a conveyer system and passed to a scoring table, comprising an air bed, conveying rollers and a scoring machine. The scoring patterns are programmed into the NC machine by a computer.

Manual labour is used to transport the scored jumbo sheets from the scoring table to a break-out table which comprises an air bed and a movable break-out bar. The glass is manoeuvred by hand so that the score line along which the glass is to be broken is positioned above the break-out bar. The bar is then raised to snap the glass. After this the cut sheets are stacked manually on frames situated randomly next to the break-out table for transportation. When a frame is loaded, the glass is secured in place and taken away and replaced by an empty frame. From studies carried out it has been found that the procedure after the glass is cut to size is inefficient as it does not follow any predefined routine. The frames are haphazardly positioned by a loader with little or no thought as to how best the frame could be positioned both in relation to other frames receiving different sizes of glass and for loading the frames both efficiently and safely.

According to one aspect of the invention there is provided sheet material handling apparatus for loading sheets on a stacking arrangement, the apparatus comprising an inspection table on which a sheet is loaded, first conveyor means for moving the sheet to one side of the table, and second conveyor means for transporting the sheet from the table towards the loading station, wherein the table has defined on it a plane which is upright relative to the surface of the table, the first conveyor means being operable to move the sheet to lie with an edge thereof parallel to the plane for monitoring at least one dimension of the sheet, the said edge of the sheet also being aligned with a lateral side of the second conveyor means.

The plane may be a physical abutment or it may be constituted by an array of sensors arranged to indicate when, for example, an edge of the sheet is aligned either coincident with it or simply parallel. The second conveyor means may include a guide defining at least the said side thereof. By aligning the sheet on the inspection table with the lateral edge of the second conveyor means, the loading from the second conveyor means onto loading means requires only longitudinal alignment as the lateral edge position is predefined.

Also according to this aspect of the invention there is provided a method of handling sheet material, for example sheet glass, comprising:

a) loading a sheet on an inspection table;

b) moving the sheet across the table by first conveyor means to align the sheet to lie with an edge thereof parallel to a plane which is upright relative to the surface of the table;

c) monitoring at least one dimension of the aligned sheet; and

d) moving the sheet onto second conveyor means for transport thereof to a loading station, the lateral aligned edge of the sheet also being aligned with a lateral side of the second conveyor means.

Preferably, the second conveyor means comprise two conveyor tracks having loading stations on opposite sides.

In this case, the first conveyor means may comprise sheet conveying means arranged to move the sheet laterally with respect to the conveyor to align the sheet with a particular track. Preferably, the conveyor is provided with sensing means, connected with the control means, for sensing the position of a sheet in relation to a specific loading station at which it is to stop and automatically slowing the conveyor down as the sheet approaches the said loading station. Each module of the conveyor is desirably independently controlled by the control means such that a plurality of different- sheets can be handled simultaneously.

Preferably, the apparatus includes measuring means arranged to produce a signal indicative of at least one dimension of the aligned sheet.

The apparatus first conveyor means may be constituted by a driven endless belt which engages the surface of the sheet to move it. The belt may be movable to either side of the surface of the table between a sheet engaging position and a disengaged position.

According to a second aspect of the invention there is provided apparatus for measuring a sheet of material, the apparatus comprising a light source arranged to illuminate the sheet, a detector, including a plurality of light sensitive elements arranged to detect reflected light defining a dimension of the sheet and processing means responsive to an output signal from the detector related to the elements receiving reflected light to derive a signal indicative of the dimension of the sheet being measured. Preferably, the light source comprises a continuous fluorescent strip light arranged to illuminate the sheet along one dimension to be measured. Alternatively, the illumination from the light source can be modified into a strip by means of a lens. For example, the light from a lamp can be modified by a lens, such as a Fresnel lens into a strip. In order to provide a particularly long strip of light a plurality of sources can be focussed in this way. Conveniently separate strips light sources, overlap in order that there are no unillu inated portions of the dimension being measured.

Preferably, the sheet is mounted on a measuring table which should be dark coloured, i.e. black, to enhance the contrast with the illuminated sheet. In order to avoid stray reflections the inspection table should be covered. In this case, the inside of the covering should be black.

The detector may be operable to detect light reflected from the sheet. Alternatively, the light may be reflected from a surface on which the sheet rests. In this case the surface should be more reflective than the sheet to produce a negative image.

Preferably, the reflected light is focussed by a lens before it is detected by the detector.

The present invention can be put into practice in various ways, one of which will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a plan of a conveyor system incorporating the present invention;

Figure 2 is a detailed view of a conveyor loading station shown in Figure 1;

Figure 3 is a side view of the station Figure 2;

Figure 4 is an end view of an inspection table in accordance with the invention; and

Figure 5 is a side view of the table of Figure 4.

Referring to Figures 1 to 3 of the drawings, a glass handling system comprises an inspection table 10 and a conveyor 12 comprising modular loading stations 14.

A programmable logic control (PLC) system controller oversees the operation of the complete system from the glass entering a break-out table 16 to the unloading of stacks of glass at a loading station 14. The sheets of glass, cut to size, are transferred onto the inspection table 10 where each is measured and then passed along the dual track conveyor system past the loading stations 14 until the appropriate loading station dealing with the appropriate size of glass is reached. The glass is then unloaded onto an awaiting glass handling frame. The glass handling frame is similar to that described in our international patent application no. PCT/GB88/00765, published as WO89/02407 The conveyor 12 is divided into the modules or loading stations 14, each of which comprises a series of drive conveyor rollers 34 driven by an electric motor 50 and a belt drive arrangment (not shown) . Each module corresponds to a stacking station. As more stacking stations are required, more modules can be added to serve them. The conveyor is conveniently used i this way to provide sufficient storage capacity . the constituents of a Jumbo sheet on each of the conveyors and the breakout table. There is also the capacity for a further two sheets further up the line, one on the scoring table and another awaiting loading on the scoring table.

Each loading station 14 comprises a pair of stacking arms 26 which run parallel to, and between, the conveyor rollers 34. Both arms 26 are rotatable together about a horizontal axis running parallel to the run of the conveyor. The pivot points for each arm 26 are located on a movable carriage which can be actuated to move the arms laterally into and out of the line of the conveyor. Each arm 26 is provided with a pair of suction cups 28 to secure the glass in place. By raising the arms about the pivot the glass is also raised and moved off the conveyor into a substantially vertical position. The arms are then slid forwardly towards a handling frame 24 for stacking. The frame on which the glass is to be stacked is mounted to rotate about a vertical axis on a turntable 36. After stacking, the arms 26 are retracted to lie substantially parallel with the conveyor rollers 34 again. Returning to the start of the progress of the glass, sheet glass that has been cut to size on the break-out table 16 is passed to the inspection table 10. There are approximately 100 different cutting combinations which can be used to divide a jumbo sheet. Typically, a sheet is cut into a maximum of nine pieces of any of four different sizes. Thus, it is necessary to identify each piece of glass as one of the four different sizes and to check its orientation for passage along the conveyor 12.

The inspection table 10 measures and correctly aligns the glass which is presented to it from the break-out table 16. The inspection table 10 comprises an air bed which has two sets of pocketed belt drives 30 and 32 which can be raised to contact the glass, or lowered to leave it partially supported by the air bed. One set of belts 30 is arranged extending transversely to the path of the conveyor 12. The other set of belts 32 extends along the path of the conveyor 12. The belt drives 30 and 32 each consist of a pair of endless rubber belts each spaced between a driven wheel and idler wheel. Each belt is movable between a retracted position in which the outer surface of the belt is below the plane of the table and a raised position in which the upper outer surface is just above the plane of the table in order to engage the glass. The belt moves between these positions within slots in the table bed. The air is fed from each of a set of conventional blowers to ports underneath the table which open into compartments within table. The air in the compartments is vented through an array of spaced air holes in the upper surface of the table. As the glass will be of different sizes, the number of air holes covered by each piece will vary. The compartmentalisation is designed to cope with this by concentrating the majority of parts in a central compartment extending laterally across the table in a position between the two slots housing the belts 30. This concentrates the lifting force in the area in which all sizes of glass will have a proportion of their area situated. A greater delivery rate of air is also required in the central region because the slots housing the belts 32 provide a greater area from which the air from the air holes can escape, undermining the lifting force in that region.

The belts 30 are driven by an electric motor (not shown) to pass the glass across the conveyor 12 into position in line with one or other of the conveyor tracks, as selected. The belts 32 pass it on to the conveyor 12.

Glass is fed onto table by hand, pushing a movable monitor flap 64 which is normally raised out of the plane of the table. The belts 32 move glass down the table until the trailing edge of the glass is past the monitor flap 64. The flap 64 rises out of the plane of the table again and thus signals by means of a microswitch that the glass has passed on to the table.

The PLC is then also arranged to raise an entry gate 62, to prevent any more sheets of glass being fed on to the table and stop and lower the longitudinal drive for the belts 32. The transverse drive belts 30 are then raised and started, driving the glass to the left-hand side of the table (as viewed from the left-hand side of Figure 1) to abut each of a set of rubber edged rollers 65 on the edge of the table.

When the glass is aligned square against the rollers 65 the condition is detected by two micro switches 60a located between two pairs of the set of rollers 65. The switches 60a signal the PLC to stop the transverse drive. The glass is thus orientated to be measured (as described later) .

After measuring, the PLC determines which side of the table the sheet should be on in accordance with the preprogrammed instructions depending on size and stacker allocation. If it is on the correct side, the transverse drive belts 30 are retracted and the longitudinal drive 32 is raised and started, driving the glass off the table toward the loading stations. The entry gate 62 is then lowered by a pneumatic piston and cylinder device (not shown) .

If the glass needs to be transferred to the opposite side of the table the transverse drive belts 30 are started in the reverse direction to drive the glass to the right hand side of the table where its position and squareness, dictated by a further set of the rollers 65, is detected by two further micro switches 60b.

When the sheet is moved to either side, contact with microswitches 60a or 60b deactuates the motor for the belt drive 30. If at any time the glass ceases to remain in contact with the relevant microswitches then the procedure is interrupted and the glass is again moved up to the rollers 65. Each set of rollers 65 does not necessarily act as a datum as such but as a convenient location at which to orientate and measure the glass.

If the glass, when it has been measured, is still deemed to be incorrectly orientated or simply a bad piece of glass by virtue of the measurement being outside predefined tolerances, the PLC actuat*- an alarm to draw the operator's attention to the situation. The operator then acknowledges the alarm by pressing a button at his operating station which disables the alarm and inhibits the movement of the sheet from the inspection table by the belts. The operator is then able to control the movement of the mis-aligned or bad piece to a convenient loading station where it can be removed by hand to restart the process and enter the, or another, piece of glass correctly onto the inspection table. It is considered safer to have the operator re-enter the glass at the start of the inspection table stage as opposed to re-aligning the glass without removing it.

As an alternative to the rollers 65 it is possible to provide a stop rail as an abutment. However, in glass handling the rollers are considered to be more suited to the abrasive nature of the edges of the material.

Control of the inspection table by the PLC is in five categories, namely a request for status, a request for information about glass size, a command to move the glass from one side of the table to the other, an emergency top command and a command to abandon a sheet of glass.

The status information can be: table empty, measuring glass, glass measured, reject glass, abandoning glass and emergency stop in effect.

A request for information regarding glass size can be made only whilst the inspection table is in the "glass measured" stage. The PLC monitors information on glass length, width and area and angle of orientation.

A command to move the glass to one side of the table or the other can also only be sent from the PLC to the inspection table whilst the inspection table 10 is in the "glass measured" state.

An emergency stop command can be sent by the system controller at any time. The emergency stop itself is implemented by a trip, which disables the system. However, the emergency stop command allows the PLC to set all outputs to a safe condition in readiness for the resumption of the process after the system is reset. This ensures that a following start-up of the system does not first cause some function to be activated which might create a dangerous situation for the operator or other attendants.

A command to reject the glass can be sent to the inspection table 10 by the PLC at any time. This command is usually used if a piece of glass is of an unrecognisable size, has an area which is below a predetermined limit, or has been entered in a bad orientation, for example at more than 45 degrees. This will be after the inspection table has measured a piece of glass and has passed this information to the PLC. The "reject glass" command can also be used as a reset after an emergency stop.

Referring to Figures 4 and 5, measurement is carried out by using an opto-electronic measuring system based on a charge-coupled device (CCD) line scan camera. In this instance an Autoscan linear photo diode array camera made by IPL Limited of Dorchester, England is fitted with a 50 mm focal length photographic lens. The lens could be a wider angle lens if a wider field of view is required, but the 50 mm focal length lens at a distance of 8 metres from the glass G is found to give an acceptable field of view of 4 metres.

Alternatively, the 8 metre distance between camera and glass could be reduced by using a wider angle lens or by more reflection of the optical path using more mirrors. It is possible to obtain wide angle lenses down to 15 mm focal lengths. With such a lens the camera-to-glass distance could be reduced to approximately 2.5 metres. This would be at the expense of reduced image quality, smaller available aperture and increased distortion. The cost of the wide angle lenses is also considerable. Because of the need to derive a measurement from the image, it is not considered advisable to reduce the focal length below about 38 mm, with a camera-to-glass distance of about 6 metres. Practically speaking, it has been found that a distance of 6 metres does not eliminate the need for reflected images. Thus, the 50 mm focal length lens is used having a high quality enlarging facility and a locked focus.

Each CCD camera has a 2840 diode array allowing a 2 mm resolution over a field of view of 4 metres. An Intel 8032 8-bit microprocessor interprets the signals detected by the array and converts them into an output for the control computer. A suitable scaling factor can be programmed into the system to enable a direct reading of object width or length. The output to the control computer is via a 4 to 2 milliamp current loop to avoid signal corruption by radio frequency interference. Each camera is mounted in an environmental housing 70 over the inspection table with an air purge system to remove dust.

Separate, independently operable cameras are used for measuring width and length. For measurement transverse to the direction of travel of the glass G, a camera 72a is positioned to receive a horizontal reflected beam of light to one side of the housing 70. A light source 74a is located on the opposite side of the housing and positioned to direct a beam of light downwardly onto the glass G to be measured. The light reflected upwardly from the glass G is in turn reflected by mirrors 76a toward the camera 72a.

Similarly, for measurement longitudinal to the direction of travel of the glass G, a camera 72b is mounted inside the hood to receive light reflected off the sheet, originating at a light source 74b. The reflected light from the sheet is reflected once more by a mirror 76b toward the camera.

The glass G is illuminated, in each case, from an angle of 30° to 45° and viewed from a similar angle by the camera. The illumination is provided by industrial fluorescent strip lamps incorporating high frequency ballasts to eliminate flicker. It is important that the strip lamp illuminates the dimension without interruption. Any "dead space" in the illumination, caused, for example, by two light sources being placed end to end, may coincide with a particular dimension of a piece of glass being measured. A single long strip lamp may be impractible. To overcome this a series of overlapping strip lamps can be used instead to provide the continuous illumination.

Another alternative is to use floodlamps. Each flood lamp comprises a 150 watt quartz halogen projector lamp and condenser lens, together with a linear Fresnel lens to focus the beam to a long narrow strip. The beams must overlap to give a uniform illumination.

In order to facilitate reliable measurement, the background (i.e. the inspection table on which the glass is supported) may be matt black. To this end, the table is covered in a black spray-on felt finish. The housing 70 covering the inspection table is painted matt black in order to avoid unwanted reflections and stray light from other sources. The measuring system could also be used on low reflectivity sheet material. However, in this case the surface supporting the sheet to be measured is reflective and the CCD camera then, effectively, detects a negative image of the illuminated surface around the sheet.

When the system is powered up, the PLC assumes that the inspection table may have glass on it, and thus any glass must be manually cleared from the table. This is the "Reject glass" state. The PLC draws the operator's attention to the "Reject glass" state. When the operator presses an "Acknowledge" push button, the alarm is muted.

The system turns on an air gate to allow the operator to move any glass from the inspection table onto the breakout table. After removing the glass, the operator presses the "Restart" button which then raises conveyor rollers 32 ready for the operator to put the next piece of glass on.

When the "break out" operator enters the next piece of glass, the belts 32 pull the glass over a measuring bridge dividing the break-out table 16 from the inspection table 10. Once the measuring routine has set a flag to say it has begun measuring, the controller raises the gate to stop subsequent sheets entering.

Once the controller has finished measuring the glass, the conveyor belts 30 used to urge the glass against the rollers 65 are lowered out of engagement with the sheet, the relative data calculated, and this information passed to the PLC. The PLC will issue an instruction to "send the sheet to an odd numbered station on the left side track", "send the sheet to an even numbered station on the right side track", or "reject the sheet". If the sheet is rejected, the PLC carries out the same procedure as for "Power up". If the sheet has to be sent to a station, the transverse belt 30 is again activated, if necessary, to move the sheet to the other side of the table to align it with the conveyor serving the targetted station. Once the limit switches 60b have signalled to say the sheet has been pushed across and squared up, the conveyor belts 30 are retracted and the longitudinal belts 32 rise to transport the sheet off the inspection table to the loading station.

The plane defined by the rollers 65 is continued on the conveyor to the loading stations by further retractable guide rollers 66. Thus, the lateral positioning of the glass along the run of one length of the conveyor 12 is determined by the inspection table 10 and maintained on the conveyor 12. The guide rollers 66 are pivotably mounted to rotate outwardly from and beneath the conveyor upper surface. The rotation is effected by pneumatic activators controlled by the PLC.

The motor 50 driving the conveyor rollers 34 is started by a signal from the PLC. A device is provided in the circuit to accelerate the "ingle phase AC motor smoothly up to speed. As the glass moves off the inspection table 10 an automatic delay is enforced which inhibits receipt of the next piece of glass to be measured until it is calculated that the inspection table is empty and ready to receive the next piece of glass.

The glass is then moved as far as possible towards the relevant stacker on the conveyor 12 with one edge up against the rollers 66 on the relevant side. The conveyor rollers 34 are slightly misaligned with respect to the overall direction of travel along the conveyor by 2°, 1° or possibly 0.5° or so in order to keep the glass hard up against the side rollers 66 of the conveyor. Alternatively, the side of each conveyor track may be fitted with a low friction wear guide. One suitable material for this is P.T.F.E.. However, again the abrasiveness of the edge of a glass sheet makes such strips probably inappropriate in this context.

As the glass passes a "slow down" sensor (not shown) , comprising a trip wheel connected to a micro switch, at each stacker, the stacker it has immediately vacated is flagged as empty thus allowing several sheets to be processed simultaneously. Once the glass has reached the relevant stacker at a loading station then that stacker is flagged as busy and is set in motion to load the glass onto a frame.

In general the glass is accelerated up to speed (1 m/s) quickly and remains at this speed until it passes the relevant trip wheel at a loading station. At this point the speed is progressively reduced to a slow speed (0.03 m/s) at hich speed it trips a retractable stop sensor to stop the glass at a corresponding loading station. The stop sensor is raised to stop the glass at its loading station under command of the PLC which will have identified the station appropriate for the dimensions of the glass. For those loading stations in the conveyor line which the glass has to pass, the stop sensor for each is retracted. Only the stop sensor for the appropriate station will be raised to stop the glass. Similarly, the slow down sensor for each loading station before the appropriate one is reached is either ignored by the PLC or disabled in order that the travelling glass is not slowed down at each station unnecessarily.

The position of the stop sensor is adjustable, under the command of the PLC, relative to the station to accommodate different lengths of glass. The stop sensor assembly comprises a retractable end-stop gate 45 which is mounted on a rodless pneumatic slide actuated by the PLC to enable the longitudinal movement. A signal from the PLC, dependent on the length of the sheet of glass to be loaded at a station, operates the pneumatic rodless piston and cylinder actuator (not shown) which shifts the position of the retractable end-stop gate 45 along the conveyor to one of a predetermined set of positions. In this case the rodless cylinder is one made by Origa Ltd of Tewkesbury, Gloucestershire, England. It comprises a pneumatically actuated piston or spool travelling in a cylinder. The position of the spool is determined by the signal from the PLC which actuates one of five proximity switches to arrest the spool in position. Thus the end stop is mounted to move with and is also positioned by, the spool.

As an alternative, the position of the end-stop sensor could be made substantially more variable by replacing the rodless cylinder and proximity switches by a worm drive and stepper motor moving the end-stop sensor under the control of the PLC. However, for the glass industry it is usually the case that only a known number of different sizes of glass will be handled.

Assuming that the glass is always at full speed when passing the "glass approaching end of travel" micro-switches, only one need be fitted, being an "up-stream" switch.

The positions of the glass downstream of this can also be generated by using a time delay within the PLC, this time delay being a function of the glass length and being triggered by the arrival of the glass at the up-stream slow-down trip wheel. This method allows alternative sizes to be catered for in the future with less mechanical adjustment of the machine, as well as being a possibly simpler and cheaper solution.

When the glass strikes a raised end-stop gate, it throws a microswitch to indicate to the PLC that it is in position for loading. The loading station microswitch stop sensors are read continuously through-out the cycle and their status stored to be transmitted back to the PLC when requested. The glass is then removed from the conveyor 12 onto the sheet glass handling frame 24 mounted on the turntable 36.

The turntable is held in a sheet receiving loading position by a pin 38. The pin 38 is mounted for axial movement on the bed 40 of the turntable 36 and is received in a recess in the rotatable part 42 of the" turntable carrying the frame when the loading position is reached. If this pin is not in place, the stacking arms 26 are prevented from moving and the operator is informed. Similarly the arms 26 will not function if no frame 24 is fitted to the relevant side of the turntable, or the frame is full; again the operator is informed of both these situations. The frame being full is monitored by the PLC keeping count of the number of sheets of glass loaded at a particular station and being arranged to inhibit further loading at that station when the count reaches a predetermined number.

When the pin 38 is pushed home the system controller looks to see whether the turntable 36 has been rotated and, if it has, it is assumed to have been emptied. If the turntable is still presenting the same face to the loading station 14 it is assumed that it has not been emptied, but has only undergone some unspecified operator intervention.

When the roller conveyor has stopped and the module 14 is required to stack glass a signal from the PLC operates further pneumatic cylinders to retract the stops and those rollers 66 in the vicinity of the loading station. When used as a temporary storage location the stops and guide rollers remain in place until the glass is ready to be moved on.

Initiation of a tilt device 46 (see Figure 3) is controlled by a Hydro-Check Model B181/S411/600 made by Schraeder Bellows Division of Parker Hannifinn pic of Cannock, Staffordshire, England actuated in response to micro-switches thrown when the end stop and guide rollers 66 are retracted. When the tilted glass on the tilt arms 26 reaches 5 degrees out of horizontal its position is detected by a micro-switch and a signal is sent to adjust pressure to the tilt cylinder 46 to hold it at that angle and to switch on a vacuum, to the suction cups 28. When the vacuum is confirmed by a vacuum switch, a signal is sent to continue movement of the glass 24 for the remaining 87 degrees of travel such that the glass will be 2° past vertical for stacking.

At some point of tilt travel, about 45 degrees, a signal is sent to operate a slide cylinder, another Hydro-Check device (Model B181/S411/450) , to initiate movement of the carriage towards the frame. Before the sheet of glass makes contact with the stack its position is detected and the cylinder speed reduced to about 0.03 metres/sec. The slide end of travel is detected by a probe which makes contact with a plate on the frame when no other glass is stacked. Thereafter the probe will contact the outer sheet of glass. The slide cylinder travel is stopped and the vacuum from the suction cups 28 released. The end of travel of the loaded arms is designed to leave the glass about 200 mm above rubber cushioning pads on the frame. When the suction is turned off the glass drops onto the pads. Once suction has been switched off a reverse pulse of air through the vacuum cups breaks the seal between the glass and cups, releasing the glass.

As the edge of the conveyor defined by the rollers 66 has already positioned the corresponding edge of the glass the PLC has only to process longitudinal alignment of the sheet. Thus the position of the transported sheet above the pads on the frame is determined by the sheet abutting the rollers 66 which are in alignment with the rollers 65 on the inspection table.

The tripped slide end of travel micro-switch is also the signal that the slide, after a short time delay, should retract. At a point on its return another micro-switch initiates the retraction of the tilt arms 26. Micro-switches also signal when the slide and tilt frames are fully retracted, restoring end stops and side guides to the vertical position and signalling to the control computer that the module is ready to accept another piece of glass.

The tilt mechanism for the stacking arms 26 is devised as a cross shaft 52 mounted on roller bearings. Keyed to each end is an arm 26 and attached to which is the rod clevis of the cylinder 46. Also fastened to the arms are the suction cups 28 and the spur gear to determine the rotational position of each arm. Each of the two arms 26 on the tilt mechanism moves through slots 56 in the conveyor. The slots 56 are also wide enough to allow the suction cups 28 to pass through. With suitable programming of the PLC it is possible to allow glass to pass along the conveyor and past a loading station even when the arms 26 are loading glass on a frame. This requires the use of additional sensors to transmit information back to the PLC to indicate whether or not the arms 26 are sufficiently raised to allow a further piece of glass to pass that loading station along the conveyor.

The suction cups are attached to a pivoting frame 58 which forms part of the tilt arms. The probe is mounted on the slide gear which is aligned to contact either a datum plate on the empty frame or the last stacked piece of glass as the slide gear advances. When contact is made, it trips a microswitch arrangement to slow down the travel. This is achieved by actuating the hydro-check unit. The slide cylinder continues to move the glass sheet towards the frame or stack for a predetermined distance until the probe is further depressed and actuates a further micro-switch arrangement causing the hydro-check to stop the slide cylinder altogether.

This feature is present so that the horizontal, retracted arms can seek the position of the stacked glass and stop when contact is made. This feature will be especially useful when the module is being used as a de-stacking unit. The horizontal slide comes forward until it touches the glass for the first time and then it will "know" a datum point. When glass is stacked the edge variation should be limited to 1 mm if possible. In order to ensure the strength of a stacked frame of glass, each separate sheet must be tightly packed against the others. This means that a frame containing 30-35 sheets could be 160 mm to 250 mm thick.

As the tilt mechanism approaches 50 degrees of rotated movement, the weight of the frame and the glass will shift from a positive load to a negative one. The tilt cylinder 46 must be controlled over all the movement of the tilt operation for position and velocity and, therefore, the hydro-check is used for this operation.

At 150 mm/second velocity, it will take approximately 5 seconds to complete the tilt action.

The horizontal slide provides the movement for placing glass onto the frame. Because there is a variation of approximately 250 mm between the position of the first sheet of glass and the last one, this mechanism may be arranged accurately to decrement a thickness of glass with each stacking operation from the horizontal travel of the tilt arms.

With an empty frame on the unloading turn-table, the tilt and slide mechanism moves and deposits the first sheet of glass. Provided that there is an empty frame mounted in position, the operator can turn the frame around. Air bearings 62 fitted to the face of the turn table 36 reduce the force needed to rotate the frame. The exact distance at which the stacking arms stop relative to the frame or the immediately previously loaded piece of glass at a particular station will also depend on the thickness of the glass being stacked. If no account is taken of this, thick glass may collide with the frame of the previously stacked piece or a thin piece of glass may be deposited too far from the frame or the last piece of glass and result in a loose stack. To overcome this the probe is provided with a series of microswitches which are successively actuated as the probe is increasingly depressed. According to the thickness of the glass being loaded which is programmed into the PLC, the microswitch is "read" which will leave the glass on the stacking arms at the correct distance from the frame or previously stacked piece. Thus, the programming of the glass thickness is arranged to set up the PLC to read only the appropriate microswitch on the probe and ignore the rest.

The batch number, glass size and customer is then printed by a ticket printer, based on information held by the PLC, on a self-adhesive label and attached to the stack of glass by the operator.

The operator covers the glass and fastens it to the frame with a strapping machine. The operator then removes it from the turntable 36 and transports it into stock. A new storage frame is loaded to await the loading operation once again.

When the system controller initiates the instruction to unload the glass it also prevents the module from stacking. The PLC communicates to the operator by light and/or sound that the module is ready for change. It also checks to see that there is an empty frame in position. If both these functions are satisfied it then allows rotation. Should either not be satisfied then this is relayed to the operator via a lamp on the operating panel. The operator takes control of the unloading by pressing a push button. This puts air to an air-bearing which allows the table to rotate. When the table 36 has rotated it is locked in position and the air-bearing is switched off. The PLC system controller then initiates the storage of a further set of sheets of glass.

All the stops, motor drives and distance measuring equipment are operated by a module interface controller related to a particular unloading area under the control of the PLC.

The stacking frames are located back-to-back on the turntable in order for a full frame to be removed whilst another is being filled. Once the turntable has been rotated, an operator can strap up the full frame; remove it from the turntable; and replace it with an empty frame, without the system being stopped.

Each turntable should be capable of storing and swinging round 2.55 m lengths of glass, therefore, the rotary path should be at least 3 m diameter. The system controller has the processing power to look after multiple tasks concurrently with an update for each task at no less than one fifth of a second intervals. The operating system allows multi-tasking operation which is transparent to the programmer. The programming language is able to handle multiple tasks concurrently whilst providing a high level programming environment. BASIC is the preferred language, however, ^»C" or "FORTH" are also acceptable.

The system controller is of industrial quality and capable of working within industrial environments. It is accessed via a console which is operable at remote locations, e.g. by a modem line, to allow modifications to the programme and system parameters to be made.

The idea is to build a handling system so that each stacking unit is a self-contained handling system. The tilt frame, slide mechanism, turntable and conveyor all combine together to form a "Stacking module". This modular approach has many advantages:- such a stacking system could be transformed into a destacking system; the transfer mechanism could be utilised for transferring glass from conveyor to conveyor; the overall concept lends itself to easy extension of the production line; and manufacturing, transportation and installation are all simplified. In addition to this the controls for each function of the module are situated on the module. This means that no further electronics are necessary when adding another module.

Due to the modular nature of the loading stations, the installation of each module is reduced to levelling the frame-work and fastening to the floor, connecting three serial communication wires, supplying the module with air, and providing mains electricity.

Each of these four separate requirements can be provided using a plug and socket. This feature allows each module to be simply bolted to the others.

This new concept is flexible in that extra modules can be added to extend the production line. It is adaptable in that it can be changed from a stacking system into a destacking system simply by changing the parameters in the set-up mode of the control computer.

Such a concept means that each module can be installed without completely disrupting production. The individual systems can be tested and commissioned on the factory floor before the line goes into production.

Each module is of known cost and can be justified in production terms for improvement in factory though-put. The modules can be placed in one single line or opposite one another in a dual line. Alternatively two lines may extend parallel, but in opposite directions from opposite sides of the inspection table or normally to one another from adjacent sides.

Claims

1. Sheet material handling apparatus for loading sheets on a stacking arrangement, the apparatus comprising an inspection table on which a sheet is loadable, first conveyor means for moving the sheet to one side of the table, at least one loading station, and second conveyor means for transporting the sheet from the table towards the loading station, wherein the table has defined on it a plane which is upright relative to the surface of the table, the first conveyor means being operable to move the sheet to lie with an edge thereof parallel to the plane for monitoring at least one dimension of the sheet, the said edge ofthe sheet also being aligned with a lateral side of the second conveyor means.

2. Apparatus as claimed in Claim 1 in which the plane is parallel to at least part of the path defined by the second conveyor means.

3. Apparatus as claimed in Claim 1 in which the second conveyor means include a guide defining at least the said lateral side thereof.

4. Apparatus as claimed in Claim 3 in which the reference plane is aligned with the one side of the second conveyor means defined by the guide.

5. Apparatus as claimed in Claim 4 in which the second conveyor means are arranged to urge the sheet against the guide as it is being transported.

6. Apparatus as claimed in claim 1 in which the second conveyor means are operable to transport the sheet from the inspection table to a selected loading station, and in which loading means are associated with at least one of the loading stations, which loading means are operable to pass the sheet from the second conveyor means to the stacking arrangement.

7. Apparatus as claimed in claim 1 in which the plane is defined by an abutment or abutments, for example, the radially outer edges of a set of wheels or rollers having axis normal to the surface of the table.

8. Apparatus as claimed in Claim 1 in which the second conveyor means are at least partially constituted by seperable conveyor modules, each module corresponding to a loading station.

9. Apparatus as claimed in Claims 1 in which the first conveyor means are operable to move the sheet for monitoring generally laterally with respect to the direction of the path of the second conveyor means.

10. Apparatus as claimed in Claim 9 in which the first conveyor means are also operable to move the sheet away from the reference plane after monitoring.

11. Apparatus as claimed in Claim 8 in which the second conveyor means define at least two conveyor paths, the first conveyor means being operable to move the sheet into alignment with sides of either of the conveyor paths.

12. Apparatus as claimed in Claim 1 in which the stacking arrangement comprises a frame which is removably mounted on a turntable adjacent the loading station, the turntable being rotatable to swing the frame between a sheet accepting position and a frame removing position.

13. Apparatus as claimed in Claim 1 including programmable control means arranged to control the first conveyor means and the second conveyor means in accordance with the measured dimensions of the sheet.